Member path helper

Provides PathHelper to read and write object member value via member path string.

• Support for Property and Field, get operations and assignment operations.
• <span style="font-weight: bold;">⚠ Breaking change: Since double quotes need to be escaped when used in strings, now use single quotes for string index keys instead.</span>

Supported operations

1. Accessing descendant properties

Example: obj.PathGet("A.B.C").

2. Array pattern indexing, and List-like types that implement the Count property and the get_Item(int) (i.e. this[int]) method

Example: obj.PathGet<string>("A.B[1].C").

3. Dictionary pattern indexing, and Dictionary-like types that implement the ContainsKey method and the get_Item (i.e. this[key]) method.

Example：obj.PathGetDefault<int?>("A.B['test'].C"), returns null if the object does not exist. Example：obj.PathGetDefault<int>("A.B['test'].C"), Returns default(int) if the object does not exist.

4. Arrays, dictionary nesting

Example:

obj.PathGet("A.B['test'][3].C")，

obj.PathGet("A.B[1][5].C")，

obj.PathGet("A.B[1]['user id'].C").

5. Member assignment

<span style="font-weight: bold;">⚠ Notice: When using the assignment operation, the path only supports class type property, class type field, value type fields, if there are value type property, the assignment is not possible, and the execution results in unchanged member values.</span>

Example: obj.PathSet("A.B['test']", "test value"), then obj.PathGet("A.B['test']") == "test value" is true Example: obj.PathSet("A.C", "abcde"), then obj.PathGet<string>("A.C") == "abcde" is true

6. Not null and Nullable mode

6.1. Not null mode

<span style="font-weight: bold;">⚠ Notice: Non-null mode requires the developer to ensure that the properties on the property path are not null, and if array or dictionary pattern is included, to also ensure that the indexed object must exist, otherwise an exception will be thrown. </span>.

When the result data type is a value type and not Nullable (such as int), a direct access expression is generated, and if there is a Nullable type in the property path, it will be accessed directly without doing a null check.

For example, when accessing the property A.B.C, where B is Nullable<MyStruct>, an expression like A.B!.Value.C

For array pattern or dictionary pattern, it is accessed directly, e.g., when accessing the array object property A.B[i].C, i < B.Count && i >= 0 is not checked. When accessing the dictionary object property A.D["my data"].C, it will not check if D["my data"] exists.

6.2. Nullable mode

<span style="font-weight: bold;">Nullable mode does not require a guarantee that the data is not null, nor does it require a guarantee that array pattern or dictionary pattern must have a value, return null when accessing the property of a non-existent object.</span>.

When the result data type is a Nullable value type or class (such as int?, string), a conditional expression is generated, and if there is a Nullable or class type in the property path, it will check for non-null before accessing, and will return null when it encounters a null object.

For example, accessing the property A.B.C, where B is Nullable<MyStruct>, will generate an expression like A.B.HasValue ? A.B.Value.C : null.

For array pattern or dictionary pattern, it will check before accessing, e.g. when accessing the array object property A.B[i].C, it will check i < B.Count && i >= 0 , and return default(T) if the check result is false. When accessing the dictionary object property A.D["my data"].C, it checks D.ContainsKey("my data"), and returns default(T) if the check result is false.

API

There are three types of generic method.

1. <T,V> : For scenarios where both item and return value (assignment)'s generic parameters are available.
2. <object, V> : For scenarios where item's generic parameter is available, but return value (assignment)'s generic parameter.
3. <object, object> : For scenarios where both item and return value (assignment)'s generic parameters are not available.

The above generic methods are extended from the non-generic methods.

Method	Description
PathExtensions.PathGet	Accesses the member value of the object.
PathExtensions.PathGetOrDefault	Accesses a member of the object, checks if the member is valid before accessing it, and returns the default value if it is invalid
PathExtensions.PathSet	Assign a value to a member of the object.
PathHelper.GetDelegate	Get the delegate method of the object member.
GetDelegateDefault	Get the nullable delegate method of an object member
GetLambda	Get the object member's lambda expression
GetLambdaDefault	Get the object member's nullable lambda expression
SetDelegate	Get the delegate method of an object member's assignment
SetLambda	Get the object member's assignment lambda expression